Method for making explosive oil impregnated sensitizer gelled aqueous explosive slurry

ABSTRACT

A process for preparing gelled aqueous explosive slurries having increased detonation velocity and sensitivity while employing densified nitrocellulose particles as the sensitizing agent is disclosed. The increase in detonation velocity and sensitivity are achieved by impregnating the densified nitrocellulose particles with an explosive oil in the form of an aqueous emulsion in which the aqueous phase is a solution of water and water-soluble oxygen-containing salt.

nited States Patent Newman [54] METHOD FOR MAKING EXPLOSIVE OIL IMPREGNATED SENSITIZER GELLED AQUEOUS EXPLOSIVE SLURRY [72] Inventor: Philip G. Newman, Kenvil, NJ.

[73] Assignee: Hercules Incorporated, Wilmington, Del.

[22] Filed: Nov. 26, 1968 [21] App]. No.: 779,240

[451 Jan. 25, 1972 Berthmann et al. 149/51 Ferguson ..l49/50 Primary Examiner-Benjamin R. Padgett Assistant Examiner-Stephen J. Lechert, Jr. Attorney-S. Grant Stewart [5 7] ABSTRACT A process for preparing gelled aqueous explosive slurries having increased detonation velocity and sensitivity while employing densitied nitrocellulose particles as the sensitizing agent is disclosed. The increase in detonation velocity and sensitivity are achieved by impregnating the densified nitrocellulose particles with an explosive oil in the form of an aqueous emulsion in which the aqueous phase is a solution of water and water-soluble oxygen-containing salt,

8 Claims, No Drawings METHOD FOR MAKING EXPLOSIVE OIL IMPREGNATED SENSITIZER GELLED AQUEOUS EXPLOSIVE SLURRY This invention relates to an improved process for preparing gelled aqueous explosive slurries employing densified nitrocellulose particles as the sensitizing agent. More particularly this invention relates to an improved process for increasing the sensitivity and detonation velocity of gelled aqueous explosive slurries by increasing the sensitivity of the nitrocellulose sensitizing agent with an explosive oil.

Aqueous explosive slurries and the processes for their preparation are well known in the art. These slurries are comprised of a sensitizing agent, an inorganic oxidizing salt, water and a gelling agent. Important factors in formulating aqueous explosive slurries are its explosive energy and sensitivity. The sensitivity and explosive energy of a slurry are dependent to a great extent upon the sensitivity, explosive energy and amount of sensitizing agent employed. Known-sensitizing agents employed in aqueous explosive slurries include among others, densified nitrocellulose particles particularly in the form of smokeless powder and explosive oils gelled with nitrocellulose and absorbed on woodpulp.

Smokeless powders to which this invention applies are the single base and double base types and are defined hereinafter. Often times the only smokeless powders which are either available or economically attractive for sensitizing aqueous explosive slurries are of the single base type. This type of smokeless powder is generally less sensitive than double base types of smokeless powder, and when employed to sensitize an aqueous explosive slurry they generally produce a slurry of lower sensitivity than if a similar amount of double base smokeless powder had been employed.

Explosive oil-sensitizing agents heretofore described are not completely satisfactory sensitizers for gelled aqueous explosive slurries since it has been found that the explosive oil separates from the gelled slurry during storage causing an unsafe condition which is especially unsafe for prepackaged slurries where long storage is anticipated. Furthermore, the processing methods suitable for preparation of these explosive oil-sensitized slurries are the cause of frequent and severe headaches for personnel preparing them due to personnel exposure to these oils.

It is the principal object of the invention to provide a process for sensitizing gelled aqueous explosive slurries with a combination of smokeless powder and explosive oils in which the disadvantages of the use of explosive oil along heretofore described are eliminated, and in which the resulting slurry has greater sensitivity and a higher detonation velocity than if smokeless powder alone had been employed as the sensitizer.

Other objects of this invention will, in part, be obvious and will, in part, appear hereinafter. For a complete understanding of the nature and objects of this invention, reference is made to the following detailed description.

The process of this invention comprises (a) preparation of an oil-in-water emulsion of an explosive oil, said emulsion comprising an oil phase comprised of explosive oil and an aqueous phase comprised of an aqueous solution of watersoluble oxygen-containing salt, (b) admixing the emulsion of step (a) with densified nitrocellulose particles for a time sufficient to provide an aqueous slurry comprised of explosive oil impregnated densified nitrocellulose, water, and oxidizing salt, and (c) admixing other slurry ingredients to this slurry following conventional explosive slurry mixing procedures to provide a gelled aqueous explosive slurry. The resulting gelled aqueous explosive slurry is more sensitive and generates increased explosive energy upon initiation as compared to a similar gelled aqueous explosive slurry in which an equivalent weight of sensitizing agent which has not been impregnated with explosive oil is employed. By the term equivalent weight of sensitizing agent" is meant the weights of the explosive oil impregnated densified nitrocellulose and nonimpregnated densified nitrocellulose are equal.

While the process of this invention is particularly useful for sensitizing single base smokeless powder with explosive oil, it is not so limited. Any form of nitrocellulose particles can be employed including densified nitrocellulose particles often referred to as smokeless powders and manufactured by any of the well-known solvent densification processes known in the art. Double base-type smokeless powder comprised of nitrocellulose and nitroglycerin and containing at least about percent by weight nitrocellulose can also be employed.

Illustrative smokeless powder formulations prepared by the well-known, conventional extrusion-type processes and contemplated as sensitizing agents in the practice of this invention are given in the table below.

Other types of densified nitrocellulose sensitizing agents prepared by solvent densification processes which can be employed are illustrated by the Fluid Ball" types of casting powder available from Olin Mathieson Corporation and having compositions as set forth in table ll.

TABLE ll TN: Type Single Base Double Base 12.6% N Nitrocellulose 98.5% 90.5% Nitroglycerin None 8.0% Z-Nitrodiphenylamine 1.50% 1.5%

Still other densified nitrocellulose particles which can be employed are prepared by the process set forth in U.S. Pat. No. 3,346,675, reference to which is hereby made.

The densified nitrocellulose particles employed in this invention can be in the form of small right cylinders, in the form of small irregularly shaped particles resulting from grinding, or they can be in the shape of small spherical, ellipsodial or irregularly shaped particles as produced by various solvent densification processes. In general it is desirable to employ nitrocellulose particles having a maximum dimension of from about 20 p. to about 2,500 Larger particle sizes can be employed, however, and the maximum size will vary depending on the configuration of the particle and its composition.

The nitrocellulose particles as heretofore described are impregnated with an oil-in-water emulsion of an explosive oil. The term oil-in-water emulsion as used herein is meant to define the emulsion formed by dispersing an explosive oil is finely divided drops within an aqueous solution comprised of water-soluble oxygen-containing salt dissolved in water. lllustrative of explosive oils which are emulsified and employed to impregnate the densified nitrocellulose particles are nitroglycerin; dinitroglycol; 1 ,2-propylene-glycoldinitrate; 1,3-propylene-glycoldinitrate; butane triol trinitrate;

diethylene glycol dinitrate; the nitrate esters of pentaerythritol', DNT oil which is a crude mixture of nitrated toluene and is comprised of mono-, diand tri-nitrotoluene; nitromethane; and the like. Mixtures of two or more of these explosive oils can be employed if desired.

Illustrative water-soluble oxygen-containing salts which when dissolved in water form the aqueous phase of the oil-inwater emulsion include ammonium nitrate, ammonium perchlorate, sodium nitrate, sodium chlorate, sodium perchlorate, potassium nitrate, potassium perchlorate, barium nitrate, calcium nitrate, calcium perchlorate, and mixtures thereof. A preferred water-soluble oxygen-containing salt for use in preparing emulsions of explosive oil is ammonium nitrate.

in preparing the aqueous solution of a water-soluble oxygen-containing salt, it is generally desirable to employ the minimum amount of water necessary to manufacture a satisfactory oil-in-water emulsion of explosive oil. The amount of water required for preparing the aqueous solution is dependent upon the solubility of the water-soluble oxygen-containing salt in water at the temperature of mixing; the solubility of the salt in water increasing with increasing temperature. In general, the aqueous solution of water-soluble oxygen-containing salt will contain at a temperature of 120 F., from about to about 30 percent by weight of water based on the weight of the aqueous solution of water-soluble oxygen-containing salt.

The oil-in-water emulsion heretofore defined is comprised of an oil phase dispersed in the aqueous solution of water-soluble oxidizing salt or aqueous phase. It is preferred to maintain the weight ratio of the aqueous phase to the oil phase in the emulsion to a value of at least about 2/ 1. Higher weight ratios can be employed. The upper limit of the weight ratio of aqueous phase to oil phase in the emulsion is dependent on the overall water content of the slurry formulation being prepared. If a high-weight ratio of aqueous phase to oil phase is employed, separation of excess water from the slurry will be necessary which can be costly and can be ineffective making the final explosive slurry composition unsuitable for its intended use.

The oil-in-water emulsions employed to impregnate densified nitrocellulose particles in accordance with this invention can be prepared employing any of the known emulsifiers, both ionic and nonionic, which are compatible with nitroglycerin and which promote formation of an oil-in-water emulsion. The preferred emulsifiers are of the nonionic type. The amount of emulsifier employed can vary from about 0.10 to about 2.0 percent by weight based on the weight of the explosive oil.

Illustrative emulsifying agents that can be employed include water-soluble hydrophilic colloids such as, for example, agaragar, gum tragacanth, gelatins and the like; water-soluble carbohydrate ethers such as methyl cellulose, low-substituted water-soluble ethyl cellulose, water-soluble glycol cellulose, hydroxyethyl cellulose and the like; water-soluble nonionic surface active agents such as the reaction products of alkylene oxide such as ethylene oxide and propylene oxide with higher fatty alcohols of about 12 to about carbon atoms in length wherein the alkoxy chain is from about six to about 20 units long; anionic surface active agents including carboxylic acid types such as soaps, including the alkali metal salts of the fatty acids which contain from about 12 to about 20 carbon atoms, the sulfuric ester-type anionic surface active agents such as sulfated alcohols of the formula ROSO Na wherein R is an alkyl group of from about eight to about 20 carbon atoms in length; cationic surface active agents such as long chain aliphatic amines and their salts such as laurylamine and laurylamine hydrochloride.

One skilled in the art can readily choose an emulsifying agent for use in making the oil-in-water emulsion defined in this invention. Long term stability of the emulsion is not necessary since the explosive oil is rapidly absorbed by the densified nitrocellulose particle during mixing.

The mixing time required for the explosive oil from the oilin-water emulsion to be completely absorbed by the densified nitrocellulose particles will vary from a few minutes up to about 1 hour. Complete absorption can be determined visually since the water phase of the emulsion will become clear following complete absorption. Source of the densified nitrocellulose, particle size, and mixing temperature are the chief factors influencing absorption rate. Absorption rate is increased with increasing mixing temperature, and is faster with smaller particle sizes of densified nitrocellulose.

In preparing an explosive slurry in accordance with this invention, the weight ratio of explosive oil in the oil-in-water emulsion to the densified nitrocellulose-sensitizing agent can vary from about 1:20 to about 1:3, and is preferably from about 1:7 to about 1:4. With weight ratios less than about 1:20 there will be insufficient explosive oil to substantially increase the sensitivity and detonation velocity of the gelled aqueous explosive slurry. With weight ratios greater than about 1:3 there will be too much explosive oil to be quickly absorbed by the densified nitrocellulose requiring long-mixing times and the possibility of separation of unabsorbed explosive oil-creating hazardous loading and packaging conditions.

Following admixing of densified nitrocellulose particles with an oil-in-water emulsion of explosive oil, conventional slurry mixing operations are followed. It is generally preferred to add any available free water of a particular slurry formation to the densified nitrocellulose particles prior to addition of the oil-in-water emulsion of explosive oil to the densified nitrocellulose. Free water is defined as the water content of a slurry formulation which is not present as moisture within solid or liquid ingredients of the slurry and which is not required to dissolve one or more solid or liquid ingredients of the slurry.

The following examples will more fully illustrate the method of this invention. All parts and percentages are by weight unless otherwise specified.

The following example illustrates preparation of small particles of densified nitrocellulose from 20 mm. single base smokeless powder for use as a sensitizing agent in an aqueous explosive slurry.

EXAMPLE 1 Conventional 20 mm. single base smokeless powder containing on a moisture free basis, 89.3 percent nitrocellulose, 9.95 percent dinitroltoluene, 0.77 percent diphenylamine, is ground under water. The resulting fine particles of densified nitrocellulose particles have the following sieve analysis:

The following examples illustrate the process of this invention and the increased detonation velocity of an aqueous explosive slurry prepared by this process.

EXAMPLE 2 About 12.8 parts of ammonium nitrate prills are dissolved in 3.2 parts of water at 140 F. To the resulting solution is added 8 parts of an explosive oil comprised of percent dinitroglycol and 20 percent nitroglycerin, 0.12 parts of diphenylamine and 0.04 parts emulsifier. This mixture is agitated in a high-speed mixer for about 1 minute whereby an oil-in-water emulsion is formed.

About 24 parts of the densified nitrocellulose particles prepared in example 1 and 4 parts of water are charged to a separate mixing bowl and slowing agitated. The emulsion is slowly added to the bowl. After about 15 minutes of mixing 0.08 parts of pine oil and 0.8 parts of natural guar gum dissolved in 2.5 parts of ethylene glycol is admixed. To this mixture is added 30.95 parts of ammonium nitrate solution (containing 18 percent water), 10 parts of sodium nitrate and 0.04 parts of cross-linked guar gum. The pH of the mixture is adjusted with acetic acid to a pH of about 5.0. Mixing is continued for about 1 minute and the resulting admixture is poured into polyethylene bags wherein it quickly forms a cohesive gelatinous mass. There is no separation of explosive oil from the gelled aqueous explosive slurry.

Tests are conducted on three explosive slurry charges prepared as described. The charges are detonated with 160 gram, 80 gram and 40 gram boosters of pentolite. For comparison purposes, a slurry is prepared employing the nitrocellulose prepared in example 1 except that there is no admixing of the densified nitrocellulose with an explosive oil. Results of the detonations are set forth in table ill.

TABLE III Composition, weight percent Explosive oil Control 1 Water 16. 16.0 Densitied nitroee1lulose. 1 32.0 32.0 Ammonium nitrate... 38. 38. 5 Sodium nitrate- 10.0 10. 0 Ethylene glycol. 2. 5 2. 5 Natural guar gum 0.8 0.8 ine 0.08 0.08 (luurgum 0.. 0.04 0.04 Final {:11 5. 2 5. 3 Densl y (grams/cc. 1.38 1.41 Confined detonation rate, meters/see.

booster 160 grams 4 5, 700 4, 700 80 grams 6, 500 4, 900 40 grams 5 5, 250 4, 660

pipe.

Tests conducted with 3 1b. sample, 2 in diameter confined in steel D D MIN The foregoing examples demonstrate the increased detonation velocity of the gelled aqueous explosive slurry sensitized with explosive oil-impregnated densified nitrocellulose over that of a slurry sensitized with the nonexplosive oil impregnated densified nitrocellulose. Employing a l60 gram pentolite booster, the detonation velocity for the slurry sensitized with explosive oil impregnated densified nitrocellulose is about 1,000 meters per second faster than that for the control slurry. Similarly, substantially improved detonation velocities are achieved employing the explosive oil sensitized nitrocellulose with both 80 and 40 gram pentolite boosters.

The explosive siurries which can be made in accordance with this invention can contain on a weight basis from about 12 to about 50 percent explosive oil impregnated densified nitrocellulose from about 25 to about 75 percent inorganic oxidizer salt and from about to about 30 percent water.

The process of this invention also provides a method for adding additional stabilizer to the nitrocellulose sensitizing agent. To add stabilizer to the nitrocellulose sensitizing agent it is only necessary to add a soluble-stabilizing agent to the explosive oil prior to preparation of the oil-in-water emulsion. When the explosive oil is absorbed into the densified nitrocellulose particle, the stabilizing agent is carried into the particle with the oil. Typical explosive oil soluble-stabilizing agents include diphenyl amine, diethyl diphenyl urea and the like. The amount of stabilizer employed is generally from 0.5 to about 2.5 percent based on the weight of the explosive oil.

The aqueous explosive siurries of this invention are in most instances insensitive to detonating action of a No. 8 commercial blasting cap, but are in all events detonable by a conventional booster charge of PETN (pentaerythritol tetranitrate),

., RP eY9i9 rimst iyistsgfim angne). FEDS;

TNT, 50/50), tetryi, composition B (RDX-TNT, 60/40), and the like.

The process of this invention provides an improvement in the preparation of aqueous explosive siurries sensitized with densified nitrocellulose since densified nitrocellulose particles, water, and explosive oil all form a part of the final aqueous explosive slurry and the detonation velocity of the resultant slurry is substantially increased. Another major advantage of the process of this invention is that a portion of the oxidizer salt of the slurry is dissolved in water and comprises the aqueous phase of the oil-in-water emulsion employed to impregnate the densified nitrocellulose particles. Thus, no separation of the explosive oil-impregnated densified nitrocellulose from the impregnating emulsion is necessary in this process. Furthermore, there is no necessity to dry the explosive oil-impregnated densified itrocellulose particles to remove water prior to their incorporation into the aqueous explosive slurry. Still another advantage of the process of this invention is that there is no separation of explosive oil from the slurry during storage.

What l claim and desire to protect by Letters Patent is:

l. in a process for preparing a gelled inorganic oxidizer salt explosive of the aqueous slurry-type containing particulate densified nitrocellulose as a sensitizing agent, the improvement providing explosive product having increased sensitivity and detonation velocity, comprising preparing an aqueous slurry of explosive oil-impregnated nitrocellulose particles, as a mixture of ingredients for said explosive product, by admixing densified nitrocellulose particles and an oil-in-water emulsion, for a time sufficient for the explosive oil to impregnate the densified nitrocellulose particles, said oil-in-water emulsion comprising an explosive oil base and an aqueous solution phase of at least one water-so uble oxygen-containing salt selected from the group consisting of ammonium nitrate, ammonium perchlorate, sodium nitrate, sodium chlorate, sodium perchlorate, potassium nitrate, potassium perchlorate, barium nitrate, calcium nitrate, and calcium perchlorate, and thereafter admixing the remaining ingredients for said explosive product with the resultant aqueous slurry to form said gelled aqueous slurry-type explosive product.

2. The process of claim 1 in which the explosive oil is a material selected from the group consisting of nitroglycerin; dinitroglycoi; l,2-propylene-glycoldinitrate; 1,3-propyleneglycoldinitrate; butane triol trinitrate; diethylene glycol dinitrate; the nitrate esters of pentaerythritol; nitrate toluene oil, nitromethane, and mixtures thereof.

3. The process of claim 2 wherein the weight ratio of the aqueous phase to the oil phase is at least about 2/1.

4. The process of claim 3 in which the weight ratio of explosive oil in oil-in-water emulsion to densified nitrocellulose is from about 1:20 to about 1:3.

5. The process of claim 4 in which the explosive oil contains an explosive oil-soluble stabilizer for nitrocellulose.

6. The process of claim 5 wherein the explosive oil is comprised of nitroglycerin and the explosive oil-soluble stabilizer is diphenyl amine.

7. The process of claim 4 wherein said densified nitrocellulose is present in the form of a single base smokeless powder.

8. The process of claim 4 wherein the densified nitrocellulose is present in the form of a double base smokeless powder comprised of at least about percent by weight of nitrocellulose. 

2. The process of claim 1 in which the explosive oil is a material selected from the group consisting of nitroglycerin; dinitroglycol; 1,2-propylene-glycoldinitrate; 1,3-propylene-glycoldinitrate; butane triol trinitrate; diethylene glycol dinitrate; the nitrate esters of pentaerythritol; nitrate toluene oil, nitromethane, and mixtures thereof.
 3. The process of claim 2 wherein the weight ratio of the aqueous phase to the oil phase is at least about 2/1.
 4. The process of claim 3 in which the weight ratio of explosive oil in oil-in-water emulsion to densified nitrocellulose is from about 1:20 to about 1:3.
 5. The process of claim 4 in which the explosive oil contains an explosive oil-soluble stabilizer for nitrocellulose.
 6. The process of claim 5 wherein the explosive oil is comprised of nitroglycerin and the explosive oil-soluble stabilizer is diphenyl amine.
 7. The process of claim 4 wherein said densified nitrocellulose is present in the form of a single base smokeless powder.
 8. The process of claim 4 wherein the densified nitrocellulose is present in the form of a double base smokeless powder comprised of at least about 85 percent by weight of nitrocellulose. 